In semiconductor production systems of various kinds for producing semiconductor products such as semiconductor integrated circuits, it is typical for operations such as CVD and etching processes to be carried out repeatedly on semiconductor wafers etc. In such instances, owing to the necessity of precisely controlling the feed of a very small amount of process gas, mass flow rate control devices such as mass flow rate controllers are employed. In the description herein below, such a mass flow rate controller is taken by way of example.
In semiconductor production systems of this type, processes involving process gases of various kinds are carried out at flow rates ranging from extremely low flows to high flows. Thus, in semiconductor production systems of this type it will be desirable to employ mass flow rate control devices that are suitable for the gases used in the respective semiconductor production systems, and that are suitable for the flow ranges in which these are used in the respective semiconductor production systems. Also, it will be preferable for the flow rate of the flow actually controlled by the flow rate control valve (hereinafter sometimes called the “actual flow rate”) to accurately accord with the mass flow rate (hereinafter sometimes simply called the “flow rate”) indicated by a flow rate setting signal. To this end, it will be desirable to perform correction of the relationship between the flow rate setting signal and the actual gas flow rate.
In one example of the prior art, a process such as the following is carried out in a semiconductor production system that includes a chamber into which a plurality of gases inflow; a plurality of mass flow rate controllers provided in association with the plurality of gases; mass flow meters for measuring flow rates of the plurality of gases; and a plurality of valves for controlling the flows of the plurality of gases. Specifically, during operation of the semiconductor production system, the plurality of valves will open and close so that the plurality of gases inflow directly into the chamber. Meanwhile, during inspection of the mass flow rate controller, actual gas flow rates will be calculated on the basis of the set flow rate of the mass controller under inspection, and a conversion factor. The opening and closing of the plurality of valves will then be controlled so that gases inflow to a mass flow meter having an optimal flow rate range, from among the plurality of mass flow meters.
In the prior art semiconductor production system described above, actual flow rates of process gases are calculated on the basis of conversion factors. Typically, in the initial state prior to shipping, the mass flow rate controller manufacturer will use a calibration gas such as nitrogen gas to adjust each mass flow rate controller so that the linearity of its actual flow rate with respect to the flow rate setting signal lies within certain reference values. However, the physical properties of the nitrogen gas that is used for the adjustment differ from the actual process gases (e.g. argon) that will actually be used in the semiconductor production system at the shipping destination. For this reason, if mass flow rate controllers that have been adjusted using nitrogen gas as the calibration gas are used without further adjustment in a semiconductor production system at the shipping destination, the problem of inability to achieve linearity with the same accuracy as with nitrogen gas may arise.
For this reason, as in the prior art discussed above, corrections are made using a single conversion factor determined beforehand for each type of gas. However, actual flows of actual process gases (hereinafter sometimes called “actual gases”) in the semiconductor production system at the shipping destination may give rise to discrepancies for which such conversion factors may not be able to fully compensate. Also, in the case of a wide full scale flow range from extremely small to large flow rates, in many instances even a mass flow rate controller that is adapted to a prescribed flow rate range will experience discrepancies in accuracy of control between a 100% full scale flow rate and a 10% full scale flow rate. In such instances as well, uniform compensation may not be possible with only a single conversion factor.
In this regard, if specialized equipment adapted to circulate a single type of gas were used in association with a mass flow rate controller adjusted for a flow rate range of a single flow rate zone, and if additionally calibration (adjustment of output characteristics of the flow rate sensor) were carried out using the actual gas, subsequent flow rate control of the actual gas would have good accuracy. However, such one-to-one correspondence between devices and types of gas is not realistic. In actual practice, given the number of different types of actual gases and of flow rate ranges, upwards of some 200 different models of mass flow rate controller would be required. This would not only present difficulties for the manufacturer, but also for the user, who would have to have maintain these different models in inventory.
With a view to addressing the above problems at least in part, an advantage of some aspects of the invention is to afford highly accurate flow rate control in a flow rate control device.
The specification of Japanese Patent Application 2006-212226 is incorporated herein by reference.